(1) Field of the Invention
This invention relates to a method for recovering cobalt compounds wherein (a) cobalt is transferred selectively into an organic extraction agent, out of solutions containing nickel and cobalt, and (b) the cobalt is then stripped into other aqueous solutions. More particularly the invention relates to a method for easily obtaining crystalline cobalt compounds, having good filtration properties, and which does not contain sodium or calcium as impurities, through the use of oxalic acid solution as a stripping agent.
(2) Prior Art
The area of material related technology has recently shown remarkable progress. In view of this rare metals, in powder form, are now extensively used in applications ranging from manufacturing articles for daily use, to producing high technology products. Such metals are also drawing much attention as valuable materials, indispensable for the development of new materials, and for the improvement of equipment performance.
The demand for cobalt in powder form is particularly strong and it is believed that it will grow further in the coming years. Nevertheless, Japan has scare recources of cobalt and almost all cobalt requirements must be covered by importation.
On the other hand, scraps containing cobalt are increasingly generated and it is an important task to insure a secured supply of cobalt resources, and to recover cobalt in powder form from super-hardened alloy, or stellite, or catalyst wastes.
The recovery of cobalt from such wastes has been achieved through the acid leaching of scraps and the separation and purification from the obtained decoction. However, nickel is often contained in the scraps along with cobalt and it is very difficult to separate the two components in order to recover cobalt. This is because both nickel and cobalt are similar in chemical properties.
Recently, however, an extraction agent has been developed that can extract and separate cobalt selectively from a solution containing cobalt and nickel, and a complete separation can be achieved without difficulty.
Various kinds of methods have been developed for such an extraction agent. All of these methods are for the separation of cobalt and nickel. Also, in most cases in the recovery of cobalt from the extraction agent, inorganic acids such as HCL, H.sub.2 SO.sub.4, HNO.sub.3, etc are used.
In the case of stripping with such inorganic acid, cobalt is released in the form of salts like CoCl.sub.2 or CoSO.sub.4. According to the conventional recovery method, alkali is added to the solution containing cobalt and the recovery is made in the form of the precipitant of cobalt hydroxide or cobalt carbonate.
The drawback of the conventional method is the formation of large amounts of salts such as NaCl, Na.sub.2 SO.sub.4, CaCl.sub.2, etc. Also, a great deal of pure water is needed to wash cobalt hydroxide or cobalt carbonate if a suitable material for a powder form product is to be obtained (600 liters of pure water is needed per kg of cobalt). Furthermore, it is extremely difficult, even with use of a large volume of pure water, to remove the salts completely.
Consequently, at the oxidation or reduction step in order to produce the cobalt in powder form, the remaining salts are decomposed and gas is generated, causing corrosion of the furnace. This is another problem faced by the conventional method. Hence, no effective method has yet been established to recover cobalt in powder form for commercial production.